I think there is something wrong with my 923A1 fuel pump....

[jedawson1]

My truck was a hard start because the fuel line was getting air in it. When it did start I would have to peddle down to get it primed and then once I let it idle it would surge up and down just like you describe. Also my truck runs great down the road.

Here are some pics, my primer tube fitting wasn't that loose, just enough to let air in. My plunger would not firm up, but right after tightened the fitting my plunger firmed up in one pull. I started at the pump and checked every fitting for snug working my way back to the tank. If you don't hit it by the tank, others have had pickup tube air leaks inside the tank which would be the next place I checked.
Plunger tube is white in the picture and my plunger is all the way out.

 

[jedawson1]

So I fixed the idle surge issue, but when I first start my truck, warm or cold, its as if its starved for fuel, i have to floor it just to keep it idling and this last about 20 seconds before it begins to catch up and the rpm's rise above idle and throttle response goes back to normal. Once it catches up it idles fine and runs fine.

I'm at a loss as to what would cause this problem especially since I have located and stopped the air leak that was causing the surging idle.

 

[M35A2-AZ]

Sounds like you still have a leak and losing a little of your prime.

 

[Hooper]

So I fixed the idle surge issue, but when I first start my truck, warm or cold, its as if its starved for fuel, i have to floor it just to keep it idling and this last about 20 seconds before it begins to catch up and the rpm's rise above idle and throttle response goes back to normal. Once it catches up it idles fine and runs fine.

I'm at a loss as to what would cause this problem especially since I have located and stopped the air leak that was causing the surging idle.

I noticed in the above picture that the pet cock looks like it is turned all the way up. That would be full open. If true your system would bleed back everytime you shut it off. I believe the TM says to burp the air by running the truck with it open so it may run fine open. If that is not it, after the truck is turned off try to open the pet cock and see if there is fuel there. I was lucky because my 925 ran perfect so I had a truck to compare to. The 925 after sitting for weeks I had fuel with a half pump. You may have already done this but thought I would mention it. It does sound like the fuel is draining back to the tank so I would expect a comprise in the system somewhere.

 

[Andyrv6av8r]

I had an issue with mine losing prime and found a leaking coupling for the fuel line. It was behind the air cleaner housing against the frame. I had to pressurize the tank and look for fuel leaking.

 

[Hooper]

So I fixed the idle surge issue, but when I first start my truck, warm or cold, its as if its starved for fuel, i have to floor it just to keep it idling and this last about 20 seconds before it begins to catch up and the rpm's rise above idle and throttle response goes back to normal. Once it catches up it idles fine and runs fine.

I'm at a loss as to what would cause this problem especially since I have located and stopped the air leak that was causing the surging idle.

That reminds me, had checking the fittings failed, plan b was to drill the fuel cap and thread in an air fitting so I could pressurize the tank. 5 psi is all you would need. There is also a diesel fuel dye you can add to increase the chances of seeing the leak.

 

[M35A2-AZ]

That reminds me, had checking the fittings failed, plan b was to drill the fuel cap and thread in an air fitting so I could pressurize the tank. 5 psi is all you would need. There is also a diesel fuel dye you can add to increase the chances of seeing the leak.

If you have the little vent line runing up the intake tower you can use that to pressurize the fuel tank. That little line is the fuel tank vent.
That is what I used to pressurize my fuel system when I was working on my m923A1.

 

[Suprman]

I bought a used fuel cap off another member and put a tire valve in it. Works great for finding leaks

 

[ARYankee]

I bought a used fuel cap off another member and put a tire valve in it. Works great for finding leaks

That's my plan as well. I just need to find one

 

[jedawson1]

I unscrewed the drain on my primer which allowed me to work the plunger in and out. There was definately air in the line (3pumps to draw fuel up to the drain valve) and this was the cause because this time I primed it up, tightened the drain screw and it fired right up without feeling like it was starving and I was able to get the RPM's up right away.

This is weird, i fixed one leak on the primer and it stoped my surging idle, but the other leak is causing the "starving for fuel" start. I'll work my way to the tank and see what I find. At least I was able to confirmed the leak is between the primer and the tank. Should be simple trouble shooting from here.

 

[Hooper]

I unscrewed the drain on my primer which allowed me to work the plunger in and out. There was definately air in the line (3pumps to draw fuel up to the drain valve) and this was the cause because this time I primed it up, tightened the drain screw and it fired right up without feeling like it was starving and I was able to get the RPM's up right away.

This is weird, i fixed one leak on the primer and it stoped my surging idle, but the other leak is causing the "starving for fuel" start. I'll work my way to the tank and see what I find. At least I was able to confirmed the leak is between the primer and the tank. Should be simple trouble shooting from here.

Dropping the tank is not so bad. Just need to siphon the fuel out first.